The present invention, in some embodiments thereof, relates to method and device of microwave spectroscopic analysis and, more particularly, but not exclusively, to method and device of ionizing radiation dosimetry.
Electron paramagnetic resonance (EPR), also denoted as electron spin resonance (ESR), is a technique used for studying chemical species that have one or more unpaired electrons, such as organic and inorganic free radicals or inorganic complexes possessing a transition metal ion.
This technique has been applied to radiation dose reconstruction, identification of irradiated food, radiation therapy, radiation processing quality assurance and archaeological dating. Tooth enamel, dentine, bone and alanine are some examples of materials successfully applied to these applications; see Desrosiers, M. F., Schauer, D. A., 2001. Electron paramagnetic resonance (EPR) biodosimetry. Nucl. Instrum. Methods B 184/1-2, 219-228, which is incorporated herein by reference.
The EPR signal of unpaired electron is acquired by an EPR spectrometer analyses a signal intercepted from a microwave magnetic field to detect the presence of unpaired electrons. Ionizing radiation generates large numbers of unpaired electron species. While most of these react immediately and disappear, in some materials in which diffusion is limited, the unpaired electrons can persist for long periods and are often related to as “paramagnetic defects”. The concentration of these radiation-induced paramagnetic defects is proportional to the absorbed dose and the EPR spectrometer measures these defects. This is performed by the resonance absorption of electromagnetic energy at electron-spin transitions when the sample is placed under external static magnetic field. In order to resolve different electron-spin levels a static magnetic field is applied. In the simplest and most typical situation unpaired electrons of free radicals have spin (or magnetic moment) equal to ½. In a magnetic field there are two magnetic levels, +½ and −½ with two different energies. The level with spin equal to −½ has less energy than the level with spin +½. The transition between these levels is possible under a resonance condition (when the applied microwave magnetic field frequency is equal to the energy difference E=hv), for example as described in David A. Schauer, Electron paramagnetic resonance (EPR) in medical dosimetry, Radiation Measurements 41 (2007) S117-S123, which is incorporated herein by reference.
Until recently the use of this technology for dosimeter was limited to isolated samples. However, recent EPR developments have made in vivo measurements possible.
Such measurements allow determining the magnitude of the exposure of individuals to ionizing radiation in a dose that could cause direct clinical effects. Currently there are several known devices and methods for in vivo EPR measurements of radiation-induced paramagnetic defects which differentiate among doses sufficiently for classifying individuals into categories for treatment, with sufficient accuracy to facilitate decisions on medical treatment.
For example, U.S. Pat. No. 7,084,628 filed on Aug. 12, 2010, describes in vivo methods and apparatus for radiation dosimetry assessment in individuals exposed to potentially harmful radiation, based on measurements in-situ of the teeth. The in vivo dosimetry assessment methods and apparatus utilize EPR techniques and employ an apparatus comprising an integrated EPR spectrometer system, an ergonomic magnet and a constructed resonator structure. This document describes a stationary dosimetry assessment apparatus which is portable as it withstands potentially adverse mechanical effects of transportation and deployment in the field. This apparatus is configured with a power supply that is compatible with both conventional AC line voltages and/or other sources of power suitable for field conditions and may be easily operated by minimally trained technicians to quickly generate a readout of estimated radiation exposure dose.